This study was conducted to evaluate changes in the composition of a poly-L-lactic D-lactic acid and trimethylene carbonate (PLDLA-TMC) sheet after insertion into the human body. A 35-year-old woman had an orbital fracture that was reconstructed using a PLDLA-TMC sheet. During iliac bone grafting for enophthalmos 190 days after the insertion, the sheet was removed and analyzed using gel permeation chromatography and Fourier transform infrared spectroscopy. The weight average molecular weight decreased (from 151,000 Da to 10,000 Da), as did the number average molecular weight (from 15,600 Da to 255 Da). An amide functional group peaks at 1,655.43 cm-1 (1,670-1,640 cm-1) and its stretch band at 1,541.26 cm-1 (1,640-1,550 cm-1) newly appeared due to serum or tissue lfuid incorporation. PLDLA-TMC is expected to exhibit favorable degradation properties.